In recent years, in the field of medicine, active development of highly effective drugs, which act directly on the affected part with less side effect, is being carried out. Particularly, a method known as drug delivery system (DDS) has attracted a great deal of attention since it allows the specific transportation of effective components such as drugs to target cells or tissues, and enables the effective component to act at the target site.
Further, in the field of molecular cell biology, gene transfer to a particular cell is recognized as an essential technology and is being studied actively. Additionally, with the recent discoveries in the genetic background of various diseases by the progress of the Human Genomic Project, the realization of such highly specific methods for gene transfer would also enable application in the field of gene therapy.
As for the method for transferring a gene into cells, a method of incorporating a macromolecular form of gene by endocytosis (calcium phosphate method, lipotectamine method, etc.), and a method for inserting a gene into a cell by perforating the cell membrane using electric pulse stimulation (electroporation or gene gun method) are known, and being used generally in molecular biology experiments.
Although these methods are convenient, they may not readily be applied in vivo, because the site to which genes are introduced must be exposed surgically by the direct and physical wounding of the cells. In addition, it is difficult to attain a gene transfer efficiency close to 100%.
Alternatively, as a highly safe method of transferring a substance, the liposome method is known. This method can be applied to cells and tissues of a living body because it does not require the injuring of the cells. However, it is difficult to give high cell and tissue specificity to liposome, which is a simple lipid. Moreover, there is another problem that the gene transfer efficiency in vivo is much lower than the required value.
Recently, a new technique of gene transfer, which uses an infectious virus created by integrating the gene of interest into the virus DNA, has been developed. This technique can be applied to individuals with approximately 100% of the gene transfer efficiency, does not require the gene transfer site to be exposed, and thus, has attracted much attention as an epoch-making method: however, there is a serious problem that the gene is transferred to cells other than the target, because the virus infects a wide range of cells non-specifically. Moreover, there is a possibility that the virus genome itself is integrated into the chromosome to induce unexpected side reaction in the future. Therefore, the technique has not yet been used therapeutically in early stages of a disease, and at present, has been applied only to patients of terminal symptoms.
In view of the above situation, the present invention was made to solve the problems of the prior art. Accordingly, the purpose of the present invention is to provide a versatile method for the safe and specific transportation and transfer of a substance (gene, protein, compound, and the like) to a target cell or tissue.